Nickel-molybdenum catalysts fabricated by mechanical alloying and spark plasma sintering

The low energy ball milling process has been used to fabricate Ni-43at.%Mo based electro-active powder. Nanometre-sized Mo particles have been embedded into an agglomerated amorphous matrix. The spark plasma sintering (SPS) process has been used to densify the powder in < 6 min at heating rates of about 250 degrees C min(-1) from 400 to 1300 degrees C, applying loads of 120 MPa. High performance porous nickel electrodes having new phases with a particle size range between 1.0 and 8.7 mu m have been obtained after rapid SPS operations. Potentiodynamic polarisation techniques have been used to characterise the hydrogen evolution reaction (HER) in KOH 30% solution at 70 degrees C. The cathodic-Tafel slopes beta c have been found from 25 to 150 mV dec(-1) and appear to decrease as the open porosity of electrodes enlarges. It has been confirmed that the larger porosity (surface roughness) of the electrodes the larger exchange current density I-0 and so their electrocatalytic activity to polarise the HER. In addition to a large surface area and a particle size distribution, the presence of metastable Ni-Mo phases coexisting with MoO2 and the existence of localised galvanic couples are remarkable features conferring the electrodes with unusual reactivity. In this study the microstructure and densification attained are reported on, as well as the preliminary polarisation analysis of these electrodes. (C) 1999 Published by Elsevier Science S.A. All rights reserved.